A communication device can be understood as an electronic device provided with appropriate communication and control capabilities for enabling use thereof for communication with others parties. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, data, multimedia and so on. A communication device typically enables a user of the device to receive and transmit communication via a communication system and can thus be used for accessing various applications.
A communication system can be seen as a facility that enables communication sessions between two or more entities such as a communication device and/or other nodes associated with the communication system. In a communication system an appropriate access system allows communication devices to access the communication system.
An access to the communications system may be provided by means of a fixed line or wireless communication interface, or a combination of these. A feature of the wireless access systems is that they allow a user thereof to move around without loosing the connection. Thus the wireless systems are typically referred to as mobile systems. It is noted, though, that in certain mobile systems the mobility may be restricted to substantially small areas, for example a house or even a room.
An example of the wireless systems is the public land mobile network (PLMN). The PLMNs are typically based on cellular technology. Examples of the cellular systems include the second generation (2G) GSM (Global System for Mobile) and the third generation (3G) systems such as systems that are based on the third Generation Partnership Project (3GPP). Wireless communications may also be provided by means of other types of systems, such as by access technologies that are added to the existing cellular infrastructures. Non-limiting examples of the additional access technologies include those known as Wimax, Long Term Evolution (LTE) and the wireless local area network (WLAN). A satellite based system is a yet further example of wireless access systems. Wireless access may also be provided by means of short range radio or other wireless links.
A communication system and a compatible communication device typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. For example, the standard or specification may define if a communication device is provided with a circuit switched carrier service or a packet switched carrier service or both. Communication protocols and/or parameters which shall be used for the connection are also typically defined. For example, the manner how the communication device can access the communication system and how communication shall be implemented between communicating devices, the elements of the communication network and/or other communication devices is typically based on predefined communication protocols.
Multi-access refers to ability to use multiple different access networks with a single communications device. The communications device may, for example, be connected to the Internet at first using a WLAN and, when outside the coverage of the WLAN network, using a cellular communications network or another access system, for example an access system based on the Wimax or Long Term Evolution (LTE).
A user of a communication device might appreciate he/she could continue an active session without interruptions, even if the communication session is transferred from an access system to another, for example due to movement of the user. This means, for example, that any applications running in a communication device and/or user of a communications device should not notice any change in the access technology or experience interruptions in the connectivity. Instead, a smooth transfer from a system to the other and continuous support of the mobility features should be provided.
The mobility features between the different access technologies may not, however, be always fully supported. Problems may occur, for example, if a user application, for example an e-mail application, starts an internet protocol (IP) session in a WLAN using for example an IPsec (IP security protocol) tunnel to a 3G network as specified by the 3GPP and then moves out of the coverage area of the WLAN. At that point the underlying communication network system, for example a general packet radio service (GPRS) system, may be used to maintain the e-mail session. However, because of the lack of any IP level mobility support, the session must be closed and re-initiated via the GPRS. Similar situation may occur when a user moves to another access technology.
A proxy mobile internet protocol (PMIP) may be employed for providing mobility for a user. The PMIP is a protocol where a communication device is not provided with any information regarding the mobility features offered by the network. Instead, the communication device operates in a simple IP manner. The simple IP is commonly understood as a reference to solutions where mobility is not offered at the internet protocol (IP) level and the device itself is not running any mobile protocols. The required mobility features are offered by an appropriate network element providing mobile internet protocol (MIP) signalling to a home agent (HA) and tunnelling between a relevant proxy mobile internet protocol (PMIP) entity and the home agent. The home agent functions to store bindings between the home address of the mobile communication device and a care-of address thereof. Based on this information the home agent may then tunnel communications to and from the mobile communication device.
A problematic situation may occur if a normal Mobile IP (MIP) is used. The term normal Mobile IP refers to applications where a client MIP is employed. In such applications the communication device controls signalling and the tunnelling as well. That is, a client MIP is employed such that a mobility management protocol runs in the communication device. Such operation includes tunnelling and causes extra overhead due to the requirement of a further IP header. For example, in the case of voice over internet protocol (VoIP) application the extra IP header might add about 20% to the overhead. Mobile IP also requires implementation of the MIP in a communication device itself, which may not always be possible or desired.
An option for providing mobility is to use a mechanism known as the Proxy MIP (PMIP). In PMIP the network and the IP mobility aspects are completely hidden from the mobile communication device. The PMIP can be used in a single access technology without terminal awareness, for example in Wimax. However, the Proxy mobile internet protocol (PMIP) may not be reliable in communication systems where it is possible to use different access technologies. More particularly, in this scenario a communication device moving from an access technology to another may need to get a new IP address from the network. If the communication device does not know anything about the mobility features offered by the network, an application cannot continue by using the IP session via a new access technology as it does not know if it belongs to the same mobility area than before.